1. Field of the Invention
The present invention relates to a color ink ribbon and a serial color printer using the same.
2. Description of the Prior Art
Some different kinds of color ink ribbons have been proposed in the past for use with a serial color printer. A first type of ribbon has a black area, cyan area, yellow area and magenta area which are arranged one after another along the length of the ribbon and each having a length greater than the width of a sheet, or spacing width, as disclosed in Japanese Patent Laid-Open Publication No. 4565/1990. A second type of ribbon is subdivided in width into four subareas each being assigned to one of cyan, yellow, and magenta ink, as proposed in Japanese Patent Publication No. 56678/1989. A third type of ribbon is divided into an upper area assigned to black and a lower area in which a yellow, magenta and cyan subareas are arranged one after another along the length of the ribbon, as taught in Japanese Utility Model Laid-Open Publication No. 102557/1989.
The first type of ribbon has a problem that it cannot print out a color image unless transported three consecutive times consuming a substantial period of time, slowing down the printing operation. Another problem is that such a ribbon cannot be efficiently used since the black areas which are usually used more frequency than the color areas have smaller dimensions than the color areas. The second type of ribbon promotes more rapid printing than the first type of ribbon. However, this type of ribbon has various problems left unsolved. Specifically, since a thermal head applicable to such a ribbon has heating elements covering only one color, the ribbon has to be shifted every time the head prints out image data in one color and, therefore, needs a complicated shifting mechanism. The ribbon prints out black image data by superposing three different colors, not only wasting time but also failing to render an image in pure black. In light of this, the ribbon may be provided with an additional area for black, and use may be made of a thermal head having heating elements covering all the four colors. Although such an implementation may enhance high speed color printing, it cannot speed up black printing since, among the heating elements covering the four colors, only the elements assigned to black can be used. In addition, this type of ribbon, like the first type of ribbon, cannot be efficiently used since the black areas thereof have smaller dimensions than the color areas. The third type of ribbon can be used more efficiently than the others since it assigns a broader dimensions to black areas which are used more frequently than the others. However, the printing speed available with this type of ribbon is low when it comes to a color printing, as with the first type of ribbon.